JP6576463B2 - Method for forming Cu plating and method for manufacturing substrate with Cu plating - Google Patents

Description

  The present invention relates to a method for forming Cu plating, a method for manufacturing a substrate with Cu plating, and a substrate with Cu plating.

  The process of forming Cu plating by electrolytic plating on a substrate has two main steps. First, a metal thin film (seed layer) for supplying electricity is formed in advance on the surface of a substrate (wafer) on which plating is to be formed. Thereafter, the substrate having the seed layer formed thereon is fixed to a power supply jig, immersed in a plating solution, and power is supplied to the seed layer to form plating (for example, Patent Document 1).

  In Patent Document 1, oxygen plasma is irradiated to the resist opening of the seed layer formed on the substrate before plating (paragraphs [0008] to [0010]). This is because a thin oxide film is formed on the surface of the seed layer by oxygen plasma irradiation to improve the wettability of the seed layer with respect to the plating solution.

JP 2006-45651 A

  The seed layer is often manufactured by raising the temperature of the deposition chamber in order to obtain a film having characteristics close to the bulk. However, when the temperature is applied to Cu, the crystal grain size (grain size) increases, so the internal stress increases, and the warp of the substrate on which the Cu seed layer is formed increases. When the warpage becomes large, the wraparound to the back surface of the substrate occurs at the time of plating, which causes a decrease in the yield of plating. Further, when the substrate is thinned, the stress increases, and the plating yield decreases.

  An object of this invention is to provide the formation method of Cu plating which improved the yield in view of said subject.

The method of forming the Cu plating of the present invention is as follows:
A first step of forming a Cu seed layer on the substrate surface such that the average crystal grain size is 50 nm or more and 300 nm or less;
A second step of forming an oxide film on the surface of the Cu seed layer in an oxygen atmosphere;
A third step of removing a portion of the oxide film;
A fourth step of supplying power to the Cu seed layer and forming Cu plating on the surface of the Cu seed layer on the oxide film side by electrolytic plating.

  According to the present invention, when the average crystal grain size of the Cu seed layer is 50 nm or more and 300 nm or less, the increase in stress can be suppressed and the warpage of the substrate can be reduced, so that the plating failure is suppressed and the plating yield is improved. be able to.

It is a cross-sectional schematic diagram for demonstrating the formation method of Cu plating of Embodiment 1. FIG. It is a process flow figure of the formation method of Cu plating of Embodiment 1. In Embodiment 1, it is a cross-sectional SIM image of the board | substrate with a plating film after forming a plating film in the method of maintaining the crystal grain diameter of a seed layer in the board | substrate with a Cu seed layer. (B) is the elements on larger scale of (a). It is a cross-sectional SIM image of the board | substrate with Cu plating in Embodiment 1. FIG. It is an etching rate comparison figure of Cu seed layer and Cu plating in Embodiment 1. It is a graph which shows the relationship between the thickness of an oxide film, and oxygen plasma processing conditions. It is a graph which shows the relationship between the contact angle of the oxide film surface formed in the surface of Cu seed layer, and the thickness of an oxide film. (A) is a surface photograph of the Cu seed layer when the thickness of the oxide film is outside the range of 5 nm to 25 nm. (B) is a surface photograph of Cu plating. (A) is a cross-sectional SEM image of the board | substrate with a plating film shown in FIG.8 (b). (B) is the elements on larger scale of (a). (A) is a surface photograph of the Cu seed layer after the oxygen plasma treatment in the first embodiment. (B) is a surface photograph of Cu plating. It is a cross-sectional SEM image of Cu seed layer shown in FIG.10 (b). (B) is the elements on larger scale of (a). It is a graph which shows the relationship between the surface roughness of the oxide film formed in the surface of Cu seed layer, and oxygen plasma processing conditions. It is a graph which shows the relationship between the thickness of the oxide film formed on a Cu seed layer, oxygen plasma processing temperature, and sample adsorption | suction moisture. (A) is the cross-sectional SEM image of the film | membrane before resist peeling in the case of forming Cu seed layer and Cu plating, without performing oxygen plasma processing. (B) is the elements on larger scale of (a). (C) is the cross-sectional SEM image of the film | membrane before resist peeling in this embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same reference numerals represent the same or corresponding parts.

[Embodiment 1]
FIG. 1 is a schematic cross-sectional view for explaining a method for forming Cu plating in the first embodiment. FIG. 2 is a process flow diagram of a Cu plating forming method according to the first embodiment.

First, a substrate 1 on which Cu electrolytic plating is to be formed is prepared (FIG. 1 (a)).
Next, a Cu seed layer 2 (feed Cu seed layer) is formed on one surface of the substrate 1 on which Cu plating is to be formed using a sputtering apparatus (FIG. 1B, first step: S10 in FIG. 2). . Here, the Cu seed layer is formed so that the average crystal grain size of the film is 50 nm or more and 300 nm or less. For example, by forming a Cu seed layer using a sputtering apparatus or the like at room temperature without using a temperature control mechanism, grain growth can be suppressed and the crystal grain size can be reduced.

  Note that the room temperature in the film formation conditions used in the present embodiment broadly means that the atmospheric temperature in the chamber at the start of film formation is room temperature (for example, 20 to 30 ° C.). Since the room temperature varies depending on the environment and use conditions, the temperature range is not limited to the above. In addition, even if the initial chamber temperature is room temperature, the film deposition temperature increases the chamber temperature by sputtering energy, so the actual film deposition temperature is above room temperature (for example, 50 to 100 ° C.) There is. When performing continuous film formation, the temperature in the film formation chamber takes over the temperature at the time of the previous film formation, and the chamber temperature at the start of film formation may be high even when the room temperature is set (for example, 30 to 80). ° C). Even in such a case, when the initial setting is a room temperature setting, this corresponds to film formation at room temperature in the present embodiment.

  Next, a resist 3 is formed on the formed Cu seed layer 2 using a photoresist (FIG. 1C). After forming the resist 3, the surface of the opening of the resist 3 of the Cu seed layer 2 formed on the substrate 1 is irradiated with oxygen plasma to form an oxide film 4 (FIG. 1 (d), second step : S20 in FIG. In this oxygen plasma treatment, the conditions of the oxygen plasma treatment are controlled so that the thickness of the oxide film 4 to be formed is 5 nm or more and 25 nm or less. In the present invention, the oxide film 4 includes a layer in which the outermost surface of Cu constituting the Cu seed layer 2 is oxidized and altered.

  Thereafter, a part of the oxide film 4 formed on the surface of the opening of the Cu seed layer 2 is removed by an etching process such as dilute sulfuric acid cleaning (FIG. 1E, third step: S30 in FIG. 2). The reason why the third step is performed is to perform surface modification by re-controlling the thickness or surface of the oxide film 4 formed in the second step to a thickness suitable for plating film formation. For the convenience of the manufacturing process, it is necessary to form an oxide film on the surface of the Cu seed layer (second process). However, in the oxygen plasma treatment of the second process, the oxide film is formed thicker than necessary. For this reason, the excess oxide film is removed by the diluted sulfuric acid cleaning in the third step.

  However, if the diluted sulfuric acid cleaning (third step) is performed, the oxide film cannot always be made thin. If the original oxide film is too thick, the removal effect cannot be exhibited. Therefore, in the oxygen plasma treatment in the second step, it is necessary to control the oxide film to be formed in a film thickness range in which the effect of dilute sulfuric acid cleaning (third step) can be exhibited. Moreover, the surface state of the oxide film 4 can be made suitable for forming a plating film in the fourth step by this third step.

  Examples of the method for removing the oxide film formed by the oxygen plasma treatment include dry etching and wet etching. The type of dry etching gas, the type of etchant used for wet etching, etc. are not particularly limited, and any removal method may be used as long as it does not adversely affect the formation of Cu plating. However, in order to enhance the wettability improvement effect of the Cu seed layer by the oxygen plasma treatment, it is preferable to perform wet etching such as dilute sulfuric acid.

  Thereafter, the substrate 1 including the Cu seed layer 2 and the oxide film 4 from which a part thereof has been removed is immersed in a plating solution, and power is supplied to the Cu seed layer 2 so that the surface of the Cu seed layer 2 on the oxide film 4 side is plated with Cu. 5 can be formed (FIG. 1 (f), fourth step: S40 in FIG. 2).

  As a step after the plating formation, the substrate 1 on which the plating has been formed may be washed by a water washing treatment. Further, an antioxidant may be applied to prevent oxidation of the surface of the Cu plating 5.

  In the present embodiment, the substrate with Cu plating can be manufactured as described above. The substrate with Cu plating includes at least a substrate and Cu plating formed on one surface thereof.

  The structure, material, shape, and the like of the substrate 1 (material to be plated) are not particularly limited, and examples of the substrate 1 include an insulator substrate and a semiconductor substrate (semiconductor wafer). Examples of the material for the semiconductor substrate include Si, SiC, and GaN.

  The substrate 1 may be, for example, a semiconductor device or a semiconductor chip manufactured using a semiconductor substrate. Examples of the semiconductor device include an IGBT (insulated gate bipolar transistor), a MOSFET (metal-oxide-semiconductor field-effect transistor), and a diode. The substrate may be a member that is used for purposes other than semiconductor devices. In addition, the shape of the material to be plated (substrate) is not limited to a wafer or a chip that is often used for a semiconductor device, and may be any size and shape that allows plating.

  The Cu seed layer 2 is a layer made of Cu. The thickness of the Cu seed layer 2 is not particularly limited as long as it is capable of supplying (feeding) electric charges and sufficiently functions as a seed layer for electrolytic Cu plating. As an example, the thickness of the Cu seed layer 2 is 300 nm.

  In addition to the Cu seed layer 2, for example, an adhesion layer may be formed between the substrate 1 and the Cu seed layer 2 for the purpose of improving the adhesion between the substrate 1 and the Cu seed layer 2. In this case, the material of the adhesion layer can be selected according to the purpose of forming the adhesion layer as long as it does not affect the formation of Cu plating. Examples of the material for the adhesion layer include Ti.

The thickness of the adhesion layer is not particularly limited as long as it does not affect the formation of Cu plating. For example, when forming an adhesion layer using Ti, the thickness of the adhesion layer is about 10 nm to 50 nm. Further, two or more adhesion layers formed between the substrate 1 and the Cu seed layer 2 may be stacked as long as they do not affect the formation of Cu plating.

  In order to exert the function as the adhesion layer, the adhesion layer is preferably formed over the entire interface between the substrate 1 and the Cu seed layer 2. When the thickness of the adhesion layer is 10 nm or less, the adhesion layer cannot be formed on the entire interface, and a region without a partial adhesion layer may be formed. Accordingly, the thickness of the adhesion layer is preferably more than 10 nm.

  In addition, what is necessary is just to set the upper limit of the thickness of an adhesion layer suitably. However, when the thickness of the adhesion layer is 100 nm or more, the function as the adhesion layer can be exhibited. However, if a film that is thicker than necessary is formed, the resistance component is increased and the device characteristics are adversely affected. For this reason, the thickness of the adhesion layer is preferably less than 100 nm, and more preferably 50 nm or less.

  As a resist material used for forming the resist 3, any type of resist may be used as long as it does not affect the formation of Cu plating, and any positive or negative resist material may be used. If it is not necessary to form a resist, the next step of oxygen plasma treatment may be performed directly on the Cu seed layer 2 without forming a resist.

  When a photoresist (photosensitive resist material) is used as the resist material, examples of the process for forming the resist 3 on the Cu seed layer 2 include the following processes. First, a photoresist is applied to the surface of the Cu seed layer 2 formed on the substrate 1, and the photoresist is uniformly spread over the entire surface of the Cu seed layer 2 by a spin coater. A photomask is placed on the photoresist uniformly spread on the substrate 1, and ultraviolet light is irradiated by an exposure machine. Then, the resist 3 can be formed by immersing the substrate 1 with a photoresist irradiated with ultraviolet rays in a developing solution and removing the resist that has not been cured.

  FIG. 3 shows a cross-section SIM of a substrate with Cu plating after forming a plating film on a substrate (substrate with a Cu seed layer) on which a Cu seed layer 2 is formed at room temperature by maintaining the crystal grain size of the seed layer. It is a statue. FIG. 3B is a partially enlarged view of FIG. As shown in FIG. 3B, the crystal grain size of the Cu seed layer 2 was measured. As a result, about 80% of the crystals had a crystal grain size of 70 to 80 nm. From this, it is considered that the average crystal grain size of this Cu seed layer is approximately 75 nm, which is a simple average of the upper and lower limits of these crystal grain sizes. Note that the strict average crystal grain size can be calculated by measuring a plurality of crystal grain sizes from the analysis result and averaging the results using an analysis method capable of observing crystal grains such as cross-sectional SIM observation.

  Thus, by forming the Cu seed layer at room temperature, the crystal grain size of the Cu seed layer can be made smaller than when the Cu seed layer is formed at a high temperature. Further, as a method for reducing the average crystal grain size of the Cu seed layer, if the Cu seed layer is formed at room temperature without using the temperature raising mechanism, the film formation time (Cu seed layer Time required for formation) can be shortened, and capital investment can be reduced, so that Cu plating can be formed at low cost and high efficiency.

  In addition, in the Cu seed layer 2, there are crystals of other sizes, for example, crystals of a size of 50 nm, 150 nm, 300 nm, etc., and it has been found that some have a maximum of 300 nm. The reason why the crystal grain size varies is that, unlike the normal growth mode, it is presumed that the crystal grains are coalesced and a large crystal grain size is formed by applying some energy.

  The coalescence of the crystal grains also depends on the thickness of the Cu seed layer to be formed, and the maximum crystal grain size increases as the thickness of the Cu seed layer increases. However, when the Cu seed layer is formed at room temperature as in the present embodiment, the growth rate of the crystal grains is drastically reduced when the thickness is 300 nm or more. Therefore, the upper limit of the crystal grain size is about 300 nm. Conceivable. In addition, when forming a film (when forming a Cu seed layer), even if the film is formed at room temperature, a certain amount of crystal growth occurs by applying sputtering energy to the film. The lower limit of the diameter is considered to be about 50 nm. From the above, the crystal grain size of the Cu seed layer is preferably 50 nm or more and 300 nm or less.

  Note that the stress of the film (Cu seed layer) increases in inverse proportion to the square of the thickness change of the substrate. For example, when the thickness of the substrate is reduced to 1/3 of the conventional thickness, the film stress is 9 times that of the conventional one. For this reason, it is more important to take measures to reduce the film stress when the film thickness is made with a thin substrate.

  As a method for reducing the stress generated by the Cu seed layer 2, it is possible to reduce the average crystal grain size of the Cu film. When the average crystal grain size is small, the stress generated due to the large number of grain boundaries is relaxed at the grain boundaries, and the stress of the entire film is reduced. On the other hand, when the average crystal grain size is increased, the grain boundary is reduced and the stress relaxation effect is reduced, so that the stress of the entire film is increased. An example of the change in film stress due to the average crystal grain size of the Cu film is a change in film stress due to the presence or absence of heat treatment performed on the Cu film.

  In the Cu sheet layer (Cu film), since the particles have energy and surface migration occurs by applying heat, the crystal grain size increases. For this reason, a Cu seed layer that has been exposed to a high temperature state and has a large crystal grain size is about 3 to 10 times as thick as a Cu seed layer formed at room temperature (without annealing) (Cu The stress of the seed layer is increased. Therefore, the stress of the film can be reduced to about 1/3 to 1/10 by keeping the average crystal grain size of the Cu seed layer at 300 nm or less. Thus, setting the average crystal grain size of the Cu seed layer to 50 nm or more and 300 nm or less is effective as a countermeasure for increasing the stress of the Cu seed layer as the substrate is thinned.

  The Cu seed layer 2 of this embodiment is a film having a smaller average crystal grain size and lower area density (film density) than Cu plating produced by electrolytic plating.

  The average crystal grain size of the Cu seed layer 2 formed as the Cu seed layer 2 is 50 nm or more and 300 nm or less as described above. As described above, as a method for forming the Cu seed layer 2 in order to set the average crystal grain size of the Cu seed layer 2 to 50 nm or more and 300 nm or less, the Cu seed layer 2 is formed without using the temperature raising mechanism of the sputtering apparatus. There is a method of setting the temperature in the chamber to room temperature. When the temperature at the time of forming the Cu seed layer 2 is set to a high temperature, the same effect as that of the above-described annealing is obtained, and the average crystal grain size increases and the stress increases.

  As described above, forming the Cu seed layer at room temperature without using a temperature raising mechanism is effective as a method for obtaining a Cu seed layer having a small average crystal grain size. And, since the film stress is reduced by forming the Cu seed layer having such a crystal grain size, the yield of Cu plating can be improved, and the Cu plating layer according to this embodiment is formed. It is possible to improve the reliability of a substrate with Cu plating, such as a semiconductor device having Cu plating.

  In the oxygen plasma treatment performed for the purpose of improving the wettability with respect to the seed layer (see Patent Document 1), if the energy of the irradiated oxygen plasma is not appropriately controlled, an oxide film is excessively formed on the Cu seed layer. Is done. An excessively formed oxide film remains at the interface as a residue (void) even after the plating is formed, and inhibits continuity between the Cu seed layer and the Cu plating. As a result, there is a problem in that the electrical characteristics and reliability are adversely affected and the plating yield is reduced. On the other hand, by setting the thickness of the oxide film to 5 nm or more and 25 nm or less, the amount of oxide film remaining after plating formation is reduced, and crystals are integrated at the interface between the Cu seed layer and Cu plating to form a good interface. Therefore, the yield of plating can be improved and the characteristics of the device (substrate with Cu plating) can be improved.

  FIG. 4 is a cross-sectional SIM image of the substrate with Cu plating after Cu plating is formed on the Cu seed layer. As shown in FIG. 4, by forming the Cu seed layer and the Cu plating using the method of this embodiment, the crystals can be integrated at the interface between the Cu seed layer and the Cu plating, and a good interface can be formed. I understand. This is an effect of performing the process of the second step so that the thickness of the oxide film formed by the oxygen plasma process on the Cu seed layer becomes 5 nm or more and 25 nm or less.

  Further, when the area density of the Cu plating is 100%, the area density of the Cu seed layer is preferably 60% or less. Thus, by reducing the area density of the Cu seed layer, the average crystal grain size of the Cu seed layer can be controlled within the range of the present embodiment. For example, the area density of the Cu seed layer can be lowered by forming the seed layer using a sputtering apparatus or the like at room temperature.

  FIG. 5 is an etching rate comparison diagram between the Cu seed layer and the Cu plating. In FIG. 5, the etching rate when Ar plasma is irradiated to each of the Cu seed layer (feeding seed layer) and Cu plating (electrolytic Cu plating film) is shown in a graph. In the present embodiment, the Cu seed layer and the Cu plating to be compared were able to form a good interface as shown in FIG. 4 (without using a temperature raising mechanism). And Cu plating formed by electrolytic plating.

  As shown in FIG. 5, the Cu plating and the Cu seed layer had different etching rates, and the etching rate of the Cu seed layer was about twice that of the Cu plating. In general, when the area density of a film is low and there are many crystal defects, bonding between atoms becomes unstable, and bonding is broken even with weaker energy, and etching is performed. For this reason, a film with a low area density has a higher etching rate when etching is performed with Ar plasma or the like than a film with a high area density. Therefore, the area density ratio can be converted from the etching rate ratio. That is, the area density ratio in this embodiment corresponds to the reciprocal of the etching rate ratio.

  As shown in FIG. 5, the etching rate of the Cu seed layer (feeding seed layer) formed so that the average crystal grain size becomes 75 nm is the etching rate of Cu plating (electrolytic Cu plating film) formed by electrolytic plating. About twice as much. From this, it is considered that the area density of the Cu seed layer is about half of the area density of the Cu plating.

  Note that the area density of the Cu film (Cu seed layer) may vary depending on the film formation conditions, and therefore it is necessary to consider an error of about 10% (± 5%). Specifically, it is necessary to consider an error of 10% (± 5%) of the etching rate and an error of 10% (± 5%) of the film quality. Even when such an error is taken into consideration, the area density of the Cu seed layer formed at room temperature is 60 when the area density of the Cu plating formed by electrolytic plating is 100% based on the ratio of the etching rate described above. % Or less.

  In addition, you may obtain | require the area density of Cu seed layer and Cu plating, for example using Rutherford backscattering analysis (RBS), the X-ray reflectivity measuring method (XRR), etc.

  FIG. 6 is a graph showing the relationship between the thickness of the oxide film formed on the Cu seed layer by the oxygen plasma treatment and the oxygen plasma treatment conditions. An RIE (reactive ion etching) apparatus was used as the plasma processing apparatus, and the oxygen plasma processing was performed by changing the value of the high frequency output (RF output) (horizontal axis in FIG. 6) and the oxygen flow rate (conditions 1 to 4). . Further, when the thickness of the natural oxide film formed on the surface of the seed layer immediately after forming the Cu seed layer and the resist on the substrate (in the state where plasma treatment is not performed) was measured, the thickness of the natural oxide film was about It was 7 nm. This film thickness is indicated by a dotted line in FIG.

  In order to obtain the wettability improving effect, which is the purpose of the oxygen plasma treatment for the Cu seed layer, it is desirable that the oxide film be uniformly formed on the entire Cu seed layer. For example, there is a valley between the crystal grains on the film surface, and it is difficult for plasma to enter and an oxide film is difficult to be formed. In order to form an oxide film in such a portion where plasma is difficult to enter, the thickness of the oxide film is preferably 5 nm or more over the entire surface of the Cu seed layer.

  Since a Cu seed layer having a large average crystal grain size and a high density is difficult to be oxidized, only an oxide film having a thickness of about 2 to 3 nm is formed even if a normal plasma treatment is performed on such a Cu seed layer.

  In addition, if the processing time of the oxygen plasma processing is increased in order to increase the thickness of the oxide film, the temperature in the plasma processing chamber is increased by the plasma energy, and the temperature of the Cu seed layer is increased, thereby increasing the stress. There is sex. For this reason, it is desirable to shorten the plasma processing time.

  The Cu film (Cu seed layer) of this embodiment formed at room temperature in order to set the average crystal grain size of the Cu seed layer to 50 nm or more and 300 nm or less is lower than normal Cu because the film density (area density) is lower. However, oxidation is likely to proceed. Therefore, an oxide film thicker than that of a conventional film having a thickness of 5 nm or more (for example, about 10 nm) can be formed on the Cu seed layer as described above, even in a short time when the temperature in the chamber does not increase. Even if the measurement error of the oxide film thickness is about 1 or 2 nm, if the thickness of the natural oxide film is 7 nm as shown in FIG. 6, the minimum thickness of the oxide film shown in FIG. It is considered to be about 5 nm.

  FIG. 7 is a graph showing the results of measuring the contact angle of the Cu seed layer that has been subjected to the oxygen plasma treatment. Conditions 1, 3 and 4 are the same as above and in FIG. From FIG. 7, it can be seen that all oxide films show good wettability in the range of 5 nm or more. Therefore, as described above, the lower limit of the thickness of the oxide film formed on the Cu seed layer after the oxygen plasma treatment is 5 nm, which is a thickness sufficient for film formation and about the thickness of the natural oxide film. preferable.

  In FIG. 6, when an excessive oxide film is formed on the Cu seed layer 2 and the color of the surface of the Cu seed layer 2 changes, it is plotted with a larger mark than the others. When an excessive oxide film is formed in this way, although it depends on the cleaning conditions in the subsequent process, a good interface as shown in FIG. 4 cannot be formed, and reliability cannot be improved by reducing stress. .

  As shown in FIG. 6, it can be seen that the thickness of the oxide film can be controlled to 5 nm or more and 25 nm or less under a plurality of oxygen plasma processing conditions even when the RF output and oxygen flow rate of the oxygen plasma processing are changed. When the oxide film formed on the Cu seed layer 2 was in the range of 5 nm or more and 25 nm or less, the surface discoloration due to excessive oxidation of the seed layer did not occur. However, when the oxide film formed on the Cu seed layer 2 was in a range of 25 nm or more, the color changed because the surface of the Cu seed layer 2 was excessively oxidized.

  Next, an evaluation test was conducted to examine the change in the dilute sulfuric acid cleaning effect depending on the thickness of the oxide film formed on the Cu seed layer. Table 1 shows the result of verifying the effect of removing the oxide film when dilute sulfuric acid is used as the remover in the third step (S30 in FIG. 2) (see FIG. 1 (e)). Cu seed layers having different oxide film thicknesses were prepared by oxygen plasma treatment, and diluted sulfuric acid cleaning was performed.

  According to the results in Table 1, the oxide film could be removed up to 25 nm, but the oxide film with a thickness of more than 25 nm (for example, 50 nm) formed excessively on the surface of the Cu seed layer could not be removed. Color remained on the membrane surface. If plating is performed with the oxide film left, the oxide film remains as a void at the interface, which affects reliability. For this reason, it is preferable to suppress the thickness of the oxide film to 25 nm or less.

  Further, from FIG. 7, when the thickness of the oxide film is in the range of 5 nm or more and 25 nm or less, the contact angle is about 15 degrees at the maximum and sufficient wettability is shown. From this, it can be seen that the oxide film formed by the oxygen plasma treatment in this embodiment has sufficient wettability and can contribute to the improvement of reliability. Therefore, the upper limit of the thickness of the oxide film formed on the Cu seed layer in this embodiment is preferably 25 nm, which is the upper limit of the thickness of the oxide film that can be removed by dilute sulfuric acid cleaning.

  FIG. 8A is a photograph of the surface of the Cu seed layer after the oxygen plasma treatment when the oxygen plasma treatment is performed on the Cu seed layer so that the thickness of the oxide film is outside the range of 5 nm to 25 nm. In the actual photograph, the surface of the Cu seed layer (of the resist opening) is excessively oxidized, so that the copper oxide is formed thick and discolored red. The substrate with the Cu seed layer shown in FIG. 8A was washed with dilute sulfuric acid and then subjected to electrolytic Cu plating to produce a substrate with Cu plating. FIG. 8B is a surface photograph of Cu plating on the substrate with the Cu seed layer. In the actual photograph, color unevenness is formed on the surface of the Cu plating.

  FIG. 9A is a cross-sectional SEM image of the substrate with the Cu plating film shown in FIG. FIG. 9A shows that a boundary line is formed at the interface between the Cu seed layer and the Cu plating. Further, in FIG. 9B, which is a partially enlarged view of FIG. 9A, voids are observed at the boundary portion. That is, the crystal continuity between the Cu seed layer and the Cu plating is hindered.

  On the other hand, FIG. 10A shows the oxygen oxygen when oxygen plasma treatment conditions are changed and oxygen plasma treatment is performed on the Cu seed layer so that oxygen plasma is irradiated to the seed layer surface with weaker energy. It is a surface photograph of Cu seed layer after plasma processing. Discoloration does not occur and excessive oxide film formation is suppressed. FIG. 10B is a photograph of the surface of the Cu plating formed after dilute sulfuric acid cleaning is performed on the Cu seed layer that has been subjected to the oxygen plasma treatment in FIG. Color unevenness does not occur in the plating.

  Further, FIG. 11A is a cross-sectional SEM image of the Cu seed layer shown in FIG. FIG. 11A shows that there is no boundary line at the interface between the Cu seed layer and the Cu plating. Moreover, in FIG.11 (b) which is the elements on larger scale of Fig.11 (a), a void is not seen in the boundary part of Cu seed layer and Cu plating. That is, the crystal continuity between the Cu seed layer and the Cu plating is maintained.

  Thus, by controlling the thickness of the oxide film within the range of 5 nm or more and 25 nm or less, generation of voids between the Cu seed layer and the Cu plating could be suppressed. From this, it can be seen that the thickness of the oxide film that can form a good interface as shown in FIG. 4 and can relieve stress and improve the reliability of the semiconductor device is 5 nm or more and 25 nm or less.

  Further, as an influence on the seed layer by irradiating the seed layer with oxygen plasma, the film surface roughness may increase due to the energy of the irradiated oxygen plasma. Increasing the surface roughness can cause defects during subsequent device fabrication, and it is desirable to confirm that the surface roughness has not increased.

  FIG. 12 shows the measurement results of the surface roughness (arithmetic average roughness Ra) in order to show how the surface roughness of the Cu seed layer after the oxygen plasma treatment changes depending on the applied oxygen plasma treatment conditions. It is a graph to show. Conditions 1, 3 and 4 are the same as in FIG. Regardless of which plasma treatment condition was used, the surface roughness was 3 nm or less. In order to prevent the occurrence of defects during device creation, the surface roughness range is preferably in the order of micrometers, and in this embodiment, it can be determined that there is no adverse effect due to the surface roughness.

  As an apparatus used for the oxygen plasma treatment of the Cu seed layer 2 shown in FIG. 1D, ICP (high frequency inductively coupled plasma), ECR (electron cyclone resonance), a parallel plate type, etc. are used in addition to RIE. It is possible.

  The processing conditions for oxygen plasma processing include parameters that can change RF output, oxygen flow rate, degree of vacuum, processing time, processing chamber size, electrode area, sample temperature during plasma processing, moisture adsorbed on the sample, etc. Is considered. By adjusting these parameters, an oxide film of 5 nm or more and 25 nm or less can be formed on the outermost surface of the Cu seed layer 2. Any processing condition may be set as long as an oxide film of 5 nm or more and 25 nm or less can be formed on the outermost surface of the Cu seed layer 2.

  FIG. 13 is a graph showing the relationship between the thickness of the oxide film formed on the Cu seed layer, the oxygen plasma treatment temperature, and the sample adsorbed moisture. Conditions other than the oxygen plasma treatment temperature (sample temperature) were fixed, and the oxygen plasma treatment was performed. A curve in which data is plotted with diamonds (with water washing) is a result of a sample in which moisture is adsorbed on the Cu seed layer 2 before the oxygen plasma treatment. A curve in which data is plotted with square marks (without water washing) is a result of a sample in which moisture adsorption was not performed on the Cu seed layer 2 before the oxygen plasma treatment.

  As shown in FIG. 13, the thickness of the oxide film formed on the Cu seed layer changed depending on the substrate temperature (plasma treatment temperature) during the oxygen plasma treatment, regardless of whether moisture was adsorbed on the Cu seed layer 2 or not. . Even when the same oxygen plasma treatment conditions were used, the thickness of the oxide film formed on the Cu seed layer changed depending on the presence or absence of moisture adsorption. However, in the processing temperature range in which the normal oxygen plasma processing is performed, such as the temperature on the horizontal axis corresponding to each plot shown in FIG. 13, an oxidation having a thickness of 5 nm to 25 nm that is effective in improving the reliability. It can be seen that a film can be formed.

  In the actual process, since a resist frame is formed on the device, it was verified whether the resist frame had an influence on the formation of the oxide film. As a result, it was found that the resist film was etched simultaneously by the oxygen plasma treatment, but the oxide film was formed normally. It has been found that the formation rate of the oxide film and the temperature dependency of the oxide film formation change due to the presence of the resist. However, this is a change that does not hinder the formation of the target oxide film of 5 nm to 25 nm. There was no effect on the oxide film formation.

  Further, since the RIE apparatus can perform anisotropic etching, there is an additional effect that the resist shape can be improved by the etching effect. FIGS. 14A and 14B show cross-sectional SEM images of the film before resist stripping when the Cu seed layer and the Cu plating are formed without performing the oxygen plasma treatment. (B) is the elements on larger scale of (a). The skirt of the resist frame spreads in the vicinity of the substrate, and the resist bites into the plating.

  On the other hand, FIG. 14C shows a cross-sectional SEM image of the film before resist stripping when oxygen plasma treatment is performed to form a Cu seed layer and Cu plating using the Cu plating forming method of this embodiment. The spread of the skirt of the resist frame is cut, and the bite into the plating is improved. If there is any bite into the plating, the adhesion of the plating is reduced, and voids are caused in the subsequent process, so improvement is necessary. As shown in FIG. 14, the oxygen plasma treatment in the present embodiment is a solution to this problem and can contribute to the improvement of reliability.

  As described above, the Cu plating forming method of the present embodiment that controls the average crystal grain size of the Cu seed layer and the thickness of the oxide film on the Cu seed layer to reduce the stress depends on the film characteristics of the Cu seed layer. Suppression of void generation and improvement of wettability at the interface between the Cu seed layer and Cu plating can be achieved at the same time without adverse effects. As a result, the reliability of the device can be improved.

  It should be thought that embodiment disclosed this time is an illustration and restrictive at no points. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  1 substrate, 2 Cu seed layer, 3 resist, 4 oxide film, 5 Cu plating.

Claims (5)

A first step of forming a Cu seed layer on one surface of the substrate such that the average crystal grain size is 50 nm or more and 300 nm or less;
A second step of forming an oxide film on the surface of the Cu seed layer in an oxygen atmosphere;
A third step of removing a portion of the oxide film;
A method of forming Cu plating, comprising: a fourth step of supplying power to the Cu seed layer and forming Cu plating on the surface of the oxide film of the Cu seed layer by electrolytic plating.   The formation method of Cu plating of Claim 1 whose thickness of the said oxide film formed at a said 2nd process is 5 nm or more and 25 nm or less.   The Cu plating layer forming method according to claim 1, wherein an area density of the Cu seed layer is 60% or less of an area density of the Cu plating.   The Cu plating layer forming method according to claim 1, wherein the Cu seed layer is formed at room temperature in the first step. A method for producing a substrate with Cu plating comprising a substrate and Cu plating formed on one surface thereof,
The said Cu plating is a manufacturing method of the board | substrate with Cu plating formed by the formation method of Cu plating of any one of Claims 1-4.